PSI - Issue 25

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L. Martelli et al. / Procedia Structural Integrity 25 (2020) 294–304 Lucrezia Martelli/ Structural Integrity Procedia 00 (2019) 000–000

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with � � � � � � � , � � � � � � � and ����� symbolising the derivative with respect to time . According to the suggested connection, the rigid coupling between the two oscillators represents the limit case of the Hooke spring in which stiffness coefficient tends to infinity �� → �� . Therefore, � → � and it is possible to verify the previous assumption of a Single-Degree-Of-Freedom (SDOF) system modifying Eq. (1) into the following one: �� � � � � � � � �� �� � � � � � � � � �� � � � � � � � � ��� � � � � �� � � (2)

Fig. 1. Coupled system: (a) structural model; (b) free body diagram for a rigid coupling (K→∞)

3. Case study On the back of the research analysed by Reggio et al. (2019), this chapter deals with the seismic response of an existing building (a multi-degree-of-freedom frame structure) and a real case study is shown to investigate how it behaves when a rigid connection links the former to an exoskeleton structure. Two types of surveys have been pursued: a linear dynamic (also called modal) analysis has allowed to obtain maximum floor displacements, among all the results; stiffness data and steel statement have been acquired by a static non-linear analysis (also known as Push-Over). 3.1 Existing structure The primary structure is part of the school complex named “De Amicis-Ruffini” which is located in Bordighera (in the province of Imperia, Italy). It is an isolated building composed by three stories over the basement, irregular floor plans and it reaches the dimensions of almost 75 m x 20 m (Fig. 2):

N

Fig. 2. Architectural plan of a standard floor

The construction dates back to the ’50s and it is a monodirectional reinforced concrete frame with lowered beams; vertical structural elements are arranged in regular interaxle spacings. Light concrete has been used for the slabs that